Leukocyte dynamics

Thursday 5 March 2009

Dr. José Borghans and Dr. Kiki Tesselaar
Research group
Our major line of research encompasses the study of leukocyte dynamics. For decades immunologists have tried to estimate the typical proliferation and death rates of diverse leukocyte populations. Even though these rates are often regarded textbook immunology, estimates easily vary by more than 100-fold. Nevertheless, these turnover rates are a key factor in our understanding of many immunological processes in health and disease. Moreover, immunologists are trying to reveal how leukocyte kinetics are disturbed in human diseases, but as long as there is controversy about leukocyte kinetics in healthy individuals, such questions remain hard to address.
Within our laboratory we use a unique interdisciplinary approach in which experiments are combined with mathematical modelling to address our research questions. In the past years we have implemented several experimental techniques, including the application of in vivo stable-isotope labelling, to measure cell production and cell loss of different cell populations. Our studies are performed in healthy (young and old) individuals, as well as in different patient populations (e.g. HIV infected individuals and patients receiving haematopoietic stem cell transplantation) to study how the dynamics of various leukocyte populations change when the immune system gets disturbed.
In patients with primary immune deficiency these studies are complemented with in depth functional and phenotypical characterization of the patient's lymphocyte compartments. In combination with genetic analyses, we aim to identify the underlying cause of the immune deficiency and determine the effects of the implicated protein(s) on immunity.

Research questions
Questions that could be addressed in a research project include:

What is the relative contribution of thymic output and peripheral proliferation to the maintenance of the peripheral T-cell pool?
• Does this change during aging and immune reconstitution?
• What is the best way to measure thymic output?

What is the turnover of the different cell types in the bone marrow?
• Is the bone marrow the reservoir for long-lived adaptive memory?
• What is the turnover of the different precursors of innate immune cells in the bone marrow?

Techniques
Cellular and molecular techniques like cell culture, Facs analysis, cell sorting, PCR. In vivo labelling experiments and GC/MS analysis. In principal projects are performed with human samples but in specific cases studies in mouse models will be performed.

Current projects
Tissue-resident memory T cells
It has recently become clear that an important part of regional immunity is provided by tissue-resident memory T cells. These cells, in contrast to memory T cells circulating in the blood, remain constrained within a particular tissue and provide fast and efficient protection to reinfection at that site. In mice, tissue-resident T cells are identified by the expression of CD69 and CD103. Due to restricted access to tissue material, much less is known about tissue-resident memory cells in humans. In this project we aim to characterize CD69+ bone-marrow and thymus-derived T cells to investigate whether these cells resemble tissue-resident memory T cells in non-lymphoid organs.

Measuring TREC contents with digital droplet PCR.
TRECs (T-cell receptor excision circles) are small fragments of circular DNA that are formed during gene rearrangement of the T cell receptor in the thymus. Since this event can only occur during T-cell development, the number of TRECs in a T-cell population gives information about the relative contribution of thymic output and peripheral T-cell proliferation to the generation of (naive) T cells. Currently we are measuring TREC numbers with a vial-based qPCR. To perform such quantifications in smaller samples, we want to switch to digital droplet qPCR. In this project you will develop and validate the digital droplet technique to measure TREC contents in T-cell subsets, and use it to compare TREC contents between different patient groups.

The role of miRNA in recent thymic emigrants (RTE).
Recent thymic emigrants (RTE) are naive T cells in the peripheral T-cell compartment that have recently been formed in the thymus. Studies in mice and neonates have shown that these cells differ from mature naive T cells, both in function and in turnover. We have performed miRNA analyses to obtain insights into the differences between RTE and mature naive T cells, and to find a marker to identify RTE. In this project you will validate the identified miRNAs and investigate their role in T cells using different techniques.

We are member of the Utrecht Center for Quantitative Immunology (http://tbb.bio.uu.nl/ucqi/), which is a unique center bringing together the expertise of immunologists, mathematical modelers and bioinformaticians. Projects can be done by shared supervision of several members of the UCQI.